JPH11326587A - Method for storing spent fuel assembly in canister - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stow spent fuels efficiently by storing in a canister the spent fuel assemblies where absorbers for neutron flux are inserted and laid out. SOLUTION: Boards 12 and 13 for absorbing neutron flux are integrally installed beforehand. An integral assembly made of boards for absorbing neutron flux is composed by providing one outer board 13 for absorbing neutron flux with (any number of) inner boards 12 for absorbing neutron flux, whose length is about a half of one side of a supporting lattice 11d. The absorbing board 12 of the assembly is inserted from one side into the spaces between the lattice 11d adjoined by a spent fuel assembly 10. Then, another assembly fabricated in a like manner is inserted from another opposite side. In this way, the assembly 10 into which the boards 12 are inserted is slowed in each sleeve. The absorbency is increased owing not only to the absorption of neutrons by the sleeves themselves but also to the absorption of strong neutrons by the boards 12 and 13 for absorbing neutrons. Even if a water gap disappears between sleeves, the subcriticality in the spent fuel assembly is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the storage of so-called spent fuel after use in a nuclear power plant, and more particularly to an improved method for efficiently storing the spent fuel in a spent fuel storage facility. is there.

[0002]

2. Description of the Related Art FIG. 4 shows a sectional structure of a conventionally used spent fuel storage facility. In this structure, spent fuel 4 is stored in a sleeve 2 made of a square pipe in a cylindrical canister 1. The sleeve 2 is laterally supported by a plurality of radial plates 3 provided in the canister 1 at a distance from each other in the axial direction. As a result, the spent fuel 4 is finally supported in the canister 1.

[0003] In this storage container structure for spent fuel 4, in order to maintain the subcriticality of the spent fuel 4, a sleeve 2
Is made of a material having excellent neutron absorption performance, such as B-SUS (boron-containing steel), and constitutes a neutron absorber. A gap is provided between the adjacent sleeves 2. Even if water enters the canister 1, neutrons are decelerated by this gap and the neutron absorption performance of the sleeve 2 is maintained to maintain subcriticality even if water enters the canister 1. be able to. That is, in order to maintain the subcriticality even when water enters, a gap for the purpose of neutron deceleration was required so as to enhance the neutron absorption performance.

[0004]

Due to this gap,
The storage efficiency of the spent fuel 4 that can be stored in one canister 1 is low, and its improvement has been desired. Accordingly, an object of the present invention is to provide a method capable of efficiently storing spent fuel.

[0005]

According to the present invention, a neutron flux absorber is provided, and the neutron flux absorber is inserted and arranged between fuel rods constituting a spent fuel assembly. A method for storing a spent fuel assembly in a container, wherein the spent fuel assembly in which an absorber is inserted is stored in a container.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts. FIG.
FIG. 2 schematically shows a spent fuel 10 fitted with a neutron flux absorber according to one embodiment of the method according to the invention,
Shows an enlarged cross section along the line II-II in FIG.

In this embodiment, in order to maintain the subcriticality of the spent fuel 10 in the storage facility, a neutron flux absorbing plate is placed at an appropriate position between the fuel rod rows of the spent fuel 10 in an area where the neutron flux distribution is strong. 12 is inserted. The neutron flux absorbing plate 12 inserted into the spent fuel 10 is made of B-SUS (boron-containing steel) in the embodiment, and has a strong neutron flux distribution region (usually in the axial direction) of the spent fuel 10. It is attached in a cantilever shape to the external neutron flux absorbing plate 13 located in the intermediate region). The neutron flux absorbing plate 13 on the outer side of the spent fuel 10 is also made of B-SUS.

In the embodiment of the present invention, the spent fuel 10
Is a used fuel assembly for a pressurized water reactor, and, as is well known, a lower nozzle 11a and an upper nozzle 11b connected by a control rod guide thimble (not shown), and a line between the nozzles 11a and 11b. A number of fuel rods 11c extending in a line and the fuel rods 1 being spaced apart in the axial direction of the fuel rods.
1c from the side.

The neutron flux absorbing plates 12 and 13 are integrally attached in advance. In this embodiment, as shown in FIG. 2, a single external neutron flux absorbing plate 13 has a plurality of sheets (three in the embodiment, but three (An arbitrary number of the neutron flux absorbers can be used depending on the number of the neutron flux absorbers). Neutron flux absorbing plate 12 of the neutron flux absorbing plate assembly
Is inserted from one side between the adjacent support grids 11d of the spent fuel assembly 10. Then, a neutron flux absorbing plate assembly, which has been similarly assembled in advance, is inserted from another side facing this one side.

The integral neutron flux absorbing plate assembly is not inserted only between a pair of adjacent support grids 11d. As shown in FIG. 1, a plurality of sets of neutron flux distribution areas are provided. It can be inserted between the support grids 11d.

The spent fuel assemblies 10 into which the neutron flux absorbing plates 12 have been inserted as described above are accommodated in the respective sleeves 2 shown in FIG. 4, but in addition to the neutron absorption by the sleeves and the like itself, the neutron flux absorption Due to the strong neutron absorption by the plates 12 and 13, the neutron absorption performance is greatly improved and the sleeve 2
It turns out that the water gap between them becomes unnecessary. That is, even if the water gap between the sleeves is eliminated, the subcriticality of the spent fuel assembly is maintained.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various modifications can be made. For example, it can be changed as follows.

1) The material of the neutron flux absorbing plate is B
Instead of SUS, other nonmetal or metal shielding materials may be used as long as the neutron absorption performance is high, or organic shielding materials made of polyethylene or other plastics may be used. Further, if the neutron flux absorbing plates 12 and 13 can be integrated, different materials may be used. 2) In the embodiment, the present invention is applied to a spent fuel assembly for a pressurized water reactor, but the present invention can be applied to other reactor type spent fuel if a neutron flux absorbing plate can be inserted. It is clear. 3) In the embodiment, the neutron flux absorbing plate is inserted from both sides of the fuel assembly, but the length of the neutron flux absorbing plate inserted into the fuel assembly is set to be substantially the same as one side of the support lattice. It may be inserted only from one side. 4) If the mounting position of the inner neutron flux absorbing plate 12 attached to the outer neutron flux absorbing plate 13 is slightly changed, as shown schematically in FIG. Can be inserted. In this case, the neutron absorption performance is further enhanced. 5) Furthermore, the neutron flux absorbing plate 13 disposed outside between the fuel rods may be omitted in some cases.

[0014]

As described above, in the method for storing a spent fuel assembly in a container according to the present invention, the neutron flux absorber is inserted between the fuel rods constituting the spent fuel assembly and the neutron flux absorber is disposed. The neutron absorption performance is improved because the spent fuel assemblies with the inserted bodies are stored in the container, and a water gap between the containers for the purpose of decelerating neutrons to effectively absorb neutrons as in the past was established. , The number of spent fuel assemblies that can be stored in the canister can be increased. That is, the storage efficiency of the spent fuel assembly in the canister can be increased, and the storage efficiency of the spent fuel assembly in the storage facility can be increased.

[Brief description of the drawings]

FIG. 1 is an elevational view showing a partially omitted general configuration of a spent fuel assembly in which a neutron flux absorbing plate is inserted according to the present invention.

FIG. 2 is a diagram schematically showing an enlarged cross section taken along line II-II of FIG. 1;

FIG. 3 is a schematic diagram showing a modified embodiment of the present invention.

FIG. 4 is a sectional view showing a canister in which a spent fuel assembly is housed in a sleeve by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Canister, 2 ... Sleeve (storage container), 10 ... Spent fuel assembly, 11c ... Fuel rod, 12 ... Neutron flux absorber (neutron flux absorber), 13 ... Neutron flux absorber (neutron flux absorber) .

Continuation of front page (72) Inventor Tadashi Hasegawa 1-1-1, Wadazakicho, Hyogo-ku, Kobe-shi, Hyogo Inside Mitsubishi Heavy Industries, Ltd.Kobe Shipyard

Claims (1)

[Claims] 1. A neutron flux absorber is prepared, said neutron flux absorber is inserted and arranged between fuel rods constituting a spent fuel assembly, and said spent fuel assembly into which said neutron flux absorber is inserted is provided. A method for storing spent fuel assemblies in a container, wherein the fuel is stored in the container.